Fluorine resins have such excellent heat resistance, chemical resistance and electrical characteristics that can never be obtained from other synthetic resins. However, because of their inactive surface, they have poor receptivity to adhesives, coatings or inks and are thus difficult to combine with other materials. Several surface treating method have hitherto been proposed for activating the surface of fluorine resins as disclosed, for example, in (1) E. R. Nelson, et al., Ind. Eng. Chem., 50, 329 (1958), (2) Tsunoda and Koishi, Kogyo Zairyo, 29 (2), 105 (1981), (3) Japanese Patent Publication No. 53-22108, and (4) Japanese Patent Publication No. 2-196834. Attention is now given to these known methods.
Method (1) is a current spread method. This method involves various operational problems arising from use of hazardous chemicals such as sodium metal and tetrahydrofuran. That is, (i) there is a danger of fire during the treatment; (ii) much care should be taken after the treatment in handling the waste solution containing complexes; (iii) the treating solution has a short working life; and (iv) fears are entertained as to environmental pollution. Besides, the treated surface undergoes a great reduction in adhesion when exposed to sunlight or heat for a long time.
Method (2) is disadvantageous in that the effect of the surface treatment on a fluorine resin is considerably lower than that obtained on polymers containing no fluorine, such as polyethylene.
Method (3), which forms unevenness on the surface of a fluorine resin, does not produce any functional group, so that the effect of surface modification is insufficient for application of adhesives having low fluidity. Further, the surface unevenness is readily lost by friction so that care should be taken in handling. Furthermore, since an apparatus to be used for the surface modification includes the vacuum system, it is large scale and the treatment speed is slow, resulting in poor productivity. In addition, a resinous component resulting from etching tends to be deposited on inner walls of the apparatus.
Method (4) uses B(CH.sub.3).sub.3 or Al(CH.sub.3).sub.3 so that the laser light irradiation should be conducted in a closed system or a reduced pressure system. As a result, the apparatus to be used is large scale, resulting in poor productivity. Moreover, these gases are highly toxic, restricting the working environment and requiring much care in handling.
In addition, since a fluorine resin generally has a very low absorption coefficient to ultraviolet and visible light, it is very difficult to induce a surface chemical reaction even when irradiated with ultraviolet light of high intensity such as a KrF excimer laser beam.